Totipotency of mouse zygotes extends to single blastomeres of embryos at the four-cell stage

Abstract

In multicellular organisms, oocytes and sperm undergo fusion during fertilization and the resulting zygote gives rise to a new individual. The ability of zygotes to produce a fully formed individual from a single cell when placed in a supportive environment is known as totipotency. Given that totipotent cells are the source of all multicellular organisms, a better understanding of totipotency may have a wide-ranging impact on biology. The precise delineation of totipotent cells in mammals has remained elusive, however, although zygotes and single blastomeres of embryos at the two-cell stage have been thought to be the only totipotent cells in mice. We now show that a single blastomere of two- or four-cell mouse embryos can give rise to a fertile adult when placed in a uterus, even though blastomere isolation disturbs the transcriptome of derived embryos. Single blastomeres isolated from embryos at the eight-cell or morula stages and cultured in vitro manifested pronounced defects in the formation of epiblast and primitive endoderm by the inner cell mass and in the development of blastocysts, respectively. Our results thus indicate that totipotency of mouse zygotes extends to single blastomeres of embryos at the four-cell stage.

Developmental capacity is unevenly distributed among single blastomeres of 2-cell and 4-cell stage mouse embryos

“…We found that the initial slight dissimilarity between early twin blastocysts increased as their development progressed, and at the late blastocyst stage, not only did the proportion of EPI cells differ but also the total number of cells, the number and fraction of TE cells, and the percentage of PE cells. This finding is consistent with the results of Maemura et al, who demonstrated that only 13% of 2-cell embryo blastomeres were able to form PE and EPI cell lineages in the ICM 55 . Similarly, Lorthongpanich et al .…”

“…Monozygotic twins resulting from the development of two separated sister blastomeres are rarely born, indicating an unequal developmental potential of blastomeres of the 2-cell embryo 4 – 9 . This observation does not contradict the totipotency of the 2-cell mouse embryo blastomeres, but suggests uneven developmental potential of the cells emerging from the first cleavage division 8 , 9 , 54 , 55 .…”

“…A single blastomere’s further reduction in developmental potential occurs after the next cleavage division. It has been shown that single blastomeres of a 4-cell embryo form blastocysts 10 , 54 , 55 ; however, after transplantation into the oviduct of a pseudopregnant foster female, their development does not result in the birth of offspring 12 . Interestingly, a recent report demonstrated that blastomeres isolated at the 4-cell stage can develop to term, but only when the number of transferred blastocysts to pseudopregnant foster females is increased to 30 per mouse 55 .…”

“…It has been shown that single blastomeres of a 4-cell embryo form blastocysts 10 , 54 , 55 ; however, after transplantation into the oviduct of a pseudopregnant foster female, their development does not result in the birth of offspring 12 . Interestingly, a recent report demonstrated that blastomeres isolated at the 4-cell stage can develop to term, but only when the number of transferred blastocysts to pseudopregnant foster females is increased to 30 per mouse 55 . Viable pups were also obtained by Zhang et al ., who aggregated individual 4-cell blastomeres with supporting embryos that lack a functional TE and ICM 18 .…”

“…This finding therefore indicates that a sufficient number of cells were provided for the blastomere-derived embryos to ensure their further development. Moreover, it has been demonstrated that isolated blastomeres of a 4-cell embryo form trophoblastic vesicles or small blastocysts consisting of only a few inner cells 10 , 54 , 55 . These results fall in line with our observation that the quadruplets had a limited ability to produce normal blastocysts containing all three cell lineages: TE, PE, and EPI.…”